Biasing conditiion of a MOS transistor

[hannover90]

Hello all,

I know about on- and off-conditions of a MOS transistor, but I don't know
what is "bias condition" of a MOS transistor.

I would be thankful if someone could explain it.

 

[erikl]

A MOSFET's bias condition describes it's (perhaps momentary) condition of conductivity, fixed by it's gate-source voltage Vgs: could be on or off, or a Vgs which stabilizes a certain impressed drain current Id, e.g. by the connection to the gate-source voltage of a current mirror.

 

[crutschow]

When using a FET as a linear amplifier it is typically biased at some drain current level that places the drain voltage at about half the supply voltage through the drain-supply resistor.
Then the collector voltage can swing ± around this bias voltage when it is amplifying an AC input signal.